Extruder and method of extrusion

ABSTRACT

An extruder includes a container having a main bore for receiving billets, a die and a piston. The container is formed with at least one gas release vent opening into the main bore at a position intermediate between the extruding end of the bore and a midpoint of the bore&#39;s length. Each gas release vent has a valve for allowing selective release of trapped gas. This structure allows venting of gases in such a manner as to allow sequential loading of billets without removal of scrap between them.

FIELD AND BACKGROUND OF THE INVENTION

[0001] The present invention relates to extrusion and, in particular, it concerns an extruder and corresponding method of extrusion which provide venting of gases in such a manner as to allow sequential loading of billets without removal of scrap between them.

[0002] Particular reference will be made below to extrusion presses fed with billets, usually aluminum billets, although it is understood that the invention can be applied to other types of presses also.

[0003] The extrusion presses for billets known at present comprise a fixed cylinder on a fixed base, inside of which cylinder a ram or main piston is movable. A movable cross member is integral with the ram, and usually guided along the base, and carries a stem extending along the extrusion axis. On the same base or another base a fixed cross member is mounted, which carries a die slide, and in the die slide various dies can be interchanged.

[0004] A so-called container having a through chamber for the billet, is movable on the base along the extrusion axis between a working position, in which it is in a sealed or tight manner against a die contained in the die slide, and a rest position, in which it is at a distance from the box which is sufficient for the passage of a shears blade moving transversely to the extrusion axis. The container is moved by cylinders located on the fixed cross member.

[0005] The presses so briefly described operate in the following manner. With the container positioned in an airtight or sealed manner against the die slide complete with a die, a billet at a suitable temperature, which has been carried onto the extrusion axis in any way whatsoever upstream of the container, is first introduced into the container and then pressed against and through the die by means of the stem; the stem moves back at the end of its run and the container is moved away from the die by the cylinders of the container, in such a way that the shears can intervene for separating the produced profile or section from the remaining part of the billet, known as the butt or scrap. The process for removal of the butt typically accounts for wastage of as much as 23% of the raw material, and greatly reduces efficiency of the extrusion cycle.

[0006] The process for preparing a press for extruding a certain quantity of aluminum alloy often leads to air being trapped in the bore of the container, before the alloy being subjected to extrusion pressure. The air is pressurized by the extrusion process and causes serious damage to the finish of the product, in the form of blisters, often accompanied by characteristic noises made by the air when it expands in the atmosphere after passing through orifices.

[0007] A standard cycle for an extrusion process, with the aim of eliminating the problem of trapped air, is called a degassing or “burp” cycle, or pre-pressing cycle. etc. According to this cycle, the aluminum alloy is compacted in the container (positioned against the die) at a pressure equal to or lower than half of the pressure required for extrusion. Such operation is called upsetting of the billet. Then the members which usually are on load during extrusion are released, that is to say, the ram, the stem, the container and the die; in other words, these members are physically moved so as to break the sealed or airtight engagement around the die, allowing air to escape. The cycle which includes degassing is then completed by closing the container once more against the die until a sealed or airtight engagement is obtained, while the main ram reassumes the position for the beginning of the extrusion.

[0008] Various systems have been proposed for improving the degassing cycle such as by provision of a valve in the stem (e.g., U.S. Pat. No. 5,311,761) or maintaining a clearance for gas to escape between the end of the container and the die (e.g., U.S. Pat. No. 5,445,004). None of these systems, however, are effective for avoiding trapping of air between a residue of a prior billet and a newly inserted billet. As a result, there remains major wastage of material and time delay due to the process of removal of the butt as described above between loading of successive billets.

[0009] An alternative approach proposed in order to minimize trapping of gases within the container is to evacuate gases from the container prior to extrusion. Examples of this approach may be found in U.S. Pat. Nos. 5,054,303 and 5,461,899. These vacuum-based implementations, however, are complicated and expensive.

[0010] There is therefore a need for an extruder and corresponding method of extrusion which provide venting of gases in such a manner as to allow sequential loading of billets without removal of scrap between them.

SUMMARY OF THE INVENTION

[0011] The present invention is an extruder and corresponding method of extrusion.

[0012] According to the teachings of the present invention there is provided, an extruder comprising: (a) a container having a main bore for receiving billets, the main bore having a loading end and an extruding end separated by a length; (b) at least one die associated with the extruding end of the main bore; and (c) a piston deployed for forcing a billet along the main bore towards the extruding end, wherein the container is formed with at least one gas release vent opening into the main bore at a position intermediate between the extruding end and a midpoint of the length, each of the gas release vents being provided with a valve deployable between an open state for allowing release of trapped gas and a closed state for preventing penetration of material from the billets into the at least one gas release vent.

[0013] According to a further feature of the present invention, the at least one gas release vent is implemented as a plurality of gas release vents spaced along at least one line between the extruding end and the midpoint of the length.

[0014] According to a further feature of the present invention, the at least one gas release vent includes a plurality of gas release vents opening into the main bore substantially along the top of the main bore.

[0015] According to a further feature of the present invention, the at least one gas release vent includes a plurality of gas release vents opening into the main bore at a plurality of different angular positions around the surface of the main bore.

[0016] According to a further feature of the present invention, the main bore has a first internal diameter adjacent to the loading end and a second internal diameter adjacent to the extruding end, the second internal diameter being larger than the first internal diameter.

[0017] According to a further feature of the present invention, the main bore has a first portion extending substantially from the loading end along at least to the midpoint, the first portion being substantially cylindrical with the first internal diameter, and wherein the main bore has a second portion extending substantially from the first portion to the extruding end, the second portion having a gradually increasing internal diameter.

[0018] According to a further feature of the present invention, the second portion has a substantially conical internal surface.

[0019] According to a further feature of the present invention, the substantially conical internal surface has a conical angle of between about 1° and about 10°.

[0020] There is also provided according to the teachings of the present invention, a method of producing an extruded pprofile using an extruder including a container with a main bore, the main bore having a loading end and an extruding end separated by a length, the container being formed with at least one selectively openable gas release vent opening into the main bore at a position intermediate between the extruding end and a midpoint of the length, the method comprising: (a) introducing into the main bore a first billet; (b) forcing the first billet towards the extruding end so as to force material from the billet through a die associated with the extruding end of the bore; (c) while material from the first billet remains within the main bore. introducing a second billet into the main bore; (d) pressing the second billet towards the material from the first billet so as to cause joining of the material from the first billet and the second billet; (e) opening the at least one gas release vent so as to release gas trapped within the main bore; and (f) forcing the second billet towards the extruding end so as to force material from both the first and second billets through the die.

[0021] According to a further feature of the present invention, the opening is performed using a plurality of gas release vents spaced along at least one line between the extruding end and the midpoint of the length.

[0022] According to a further feature of the present invention, the opening is performed using a plurality of gas release vents opening into the main bore substantially along the top of the main bore.

[0023] According to a further feature of the present invention, the opening is performed using a plurality of gas release vents opening into the main bore at a plurality of different angular positions around the surface of the main bore.

[0024] According to a further feature of the present invention, the main bore has a larger internal diameter adjacent to the extruding end than adjacent to the loading end.

[0025] According to a further feature of the present invention, the main bore has a portion of gradually increasing internal diameter from a location between the midpoint and the extruding end extending substantially to the extruding end.

[0026] According to a further feature of the present invention, the second portion has a substantially conical internal surface.

[0027] According to a further feature of the present invention, the substantially conical internal surface has a conical angle of between about 1° and about 10° .

[0028] According to a further feature of the present invention, each billet is prepared prior to introduction into the main bore by removing material from at least a portion of an outer surface of the billet so as to increase smoothness of the billet.

[0029] According to a further feature of the present invention, the billets are aluminum billets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

[0031]FIG. 1 is a schematic partially cut-away side view of an extruder. Constructed and operative according to the teachings of the present invention, after insertion of a first billet into the main bore of the container;

[0032]FIG. 2 is an enlarged view of the container of FIG. 2;

[0033]FIG. 3 is a view similar to FIG. 1 after insertion of a second billet; and

[0034]FIG. 4 is a view similar to FIG. 3 after conjoining of the second billet with material from the fist billet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention is an extruder and corresponding method of extrusion.

[0036] The principles and operation of extruders and corresponding methods according to the present invention may be better understood with reference to the drawings and the accompanying description.

[0037] Referring now to the drawings, FIGS. 1-4 show an extruder. generally designated 10, constructed and operative according to the teachings of the present invention. Generally speaking, extruder 10 includes a container 12 having a main bore 14 with a loading end 16 for receiving billets 18. At least one die 20 associated with an extruding end 22 of main bore 14, while a piston 24 is deployed for forcing a billet 18 along main bore 14 towards extruding end 22, all as is known in the art.

[0038] It is a particular feature of extruders according to the present invention that container 12 is formed with at least one gas release vent 26 opening into main bore 14 at a position intermediate between extruding end 22 and a midpoint 28 of the length of bore 14. Each gas release vent 26 is provided with a valve 30 deployable between an open state for allowing release of trapped gas and a closed state for preventing penetration of material from the billets into the at least one gas release vent.

[0039] In order to maximize the efficiency of gas release, extruder 10 preferably includes multiple gas release vents 26. Specifically, in the preferred example illustrated here, gas release vents 26 are spaced along one or more lines between the extruding end 22 and midpoint 28. In some preferred cases, there may be an advantage to positioning vents 26 substantially along the top of main bore 14. Most preferably, a plurality of gas release vents 26 open into main bore 14 at a plurality of different angular positions around the surface of the bore, for example, with a line of vents 26 as shown along the top and bottom, and similarly along both sides (not shown), of bore 14.

[0040] Valves 30 may be of any type suited to the operational conditions (temperature and pressure) within bore 14. Typically, a small displacement valve of the type used in internal combustion engines is suitable. The displacement required to efficiently allow escape of pressurized trapped gases is typically of the order of about a millimeter or less. Actuation of valves 30 is typically achieved via a small actuator rod (not shown) passing along the bore of each vent 26 and spring-biased to return to its closed position. Opening of valves 30 may be performed simultaneously or sequentially, initiated automatically or manually, by any suitable control mechanism as will be clear to one ordinarily skilled in the art. Details of a control mechanism do not constitute part of the claimed invention and will not be described here.

[0041] According to a further preferred feature of the present invention, main bore 14 has a first internal diameter 32 adjacent to loading end 16 and a second internal diameter 34 adjacent to extruding end 22, where second internal diameter 34 is larger than first internal diameter 32. Specifically, a first portion 36 of main bore 14, extending substantially from loading end 16 along at least to midpoint 28, is preferably substantially cylindrical, while a second portion 38. extending substantially from the first portion to extruding end 22, preferably exhibits a gradually increasing internal diameter. This region of increasing diameter is preferably limited to the third of bore 14 proximal to extruding end 22, and most preferably lies within the quarter of the length nearest extruding end 22. Most preferably, second portion 38 has a substantially conical internal surface with a conical angle (defined as the inclination relative to a central axis of symmetry) of between about 1° and about 10°, and preferably no more than about 5°. The presence of portion 38 with a gradually increasing diameter has been found to be highly effective at localizing trapped gases within that region, thereby facilitating their efficient release via vents 26.

[0042] Turning now to the operation of extruder 10 and the corresponding method of the present invention, a first billet 18 is first introduced into main bore 14 as shown in FIGS. 1 and 2. Extrusion then proceeds in a conventional manner, typically with a “burp cycle” which may optionally also include opening of valves 30 if required, followed by extrusion with piston 24 driving material from billet 18 through die 20 to produce an extruded article 40. Then, at the end of a required length of extrusion when a relatively small portion of the first billet material is left, piston 24 is withdrawn and a second billet 18′ is introduced into main bore 14 (FIG. 3). This is done without the conventional step of opening the container and cutting away the butt of first billet 18. The second billet 18′ is then pressed towards the material from the first billet 18 so as to cause conglomeration of the material from the first billet and the second billet. This typically occurs at pressures lower than the extrusion pressure, such as, for example, the conditions used for upsetting of the billet as mentioned above. At this stage, valves 30 are opened so as to release trapped gas via vents 26. Optionally, the container may also be opened very slightly in the same manner as during a normal “burping cycle” to additionally release any gases which may have become trapped at the end of bore 14. Extrusion then proceeds as before with piston 24 forcing material from both the first and second billets through the die. The loading, pressing, gas release and extruding steps may then be repeated again and again without requiring opening of the container or disposal of residual material until the end of the extrusion session.

[0043] According to a further preferred feature of the method of the present invention, each billet is prepared prior to introduction into the main bore by removing material from at least a portion of an outer surface of the billet so as to increase smoothness of the billet. This preparation serves a double purpose. Firstly, smoothing of the billet facilitates passage of gases along spaces between the billet and internal surfaces of bore 14. thereby avoiding the formation of isolated gas pockets which might not reach vents 26. Additionally, “scalping” of the billets removes a large proportion of oxides and other impurities which are typically present in surface layers of billets. This enhances the quality and uniformity of the extruded product.

[0044] Devices and methods for billet scalping per se are well known in the art and will not be dealt with here in detail. Most preferably. conventional metal cutting techniques such as milling techniques may be used to remove an outer layer of a substantially cylindrical billet to provide a high quality highly cylindrical billet. The total quantity removed is typically no more than about 5%, and more preferably no more than about 2%, of the total material of the billet. ensuring that the wastage is clearly outweighed by the much larger savings in raw materials resulting from the use of the “butt” of each billet.

[0045] It will be noted that this extruder and the extrusion method facilitated thereby offer numerous profound advantages when compared to conventional techniques. Firstly, huge savings in both time and raw materials are afforded by enabling use of residual material from a previous billet conglomerated with a subsequent billet without the problems of trapped gases. Additionally, since the remainder of a billet is not discarded, the operator has much greater flexibility to choose at what point to stop the extrusion for loading a new billet. This allows stops to be planned at the end of required lengths of extruded products, thereby further reducing wastage.

[0046] It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope of the present invention. 

What is claimed is:
 1. An extruder comprising: (a) a container having a main bore for receiving billets, said main bore having a loading end and an extruding end separated by a length; (b) at least one die associated with said extruding end of said main bore; and (c) a piston deployed for forcing a billet along said main bore towards said extruding end, wherein said container is formed with at least one gas release vent opening into said main bore at a position intermediate between said extruding end and a midpoint of said length, each of said gas release vents being provided with a valve deployable between an open state for allowing release of trapped gas and a closed state for preventing penetration of material from the billets into said at least one gas release vent.
 2. The extruder of claim 1, wherein said at least one gas release vent is implemented as a plurality of gas release vents spaced along at least one line between said extruding end and said midpoint of said length.
 3. The extruder of claim 1, wherein said at least one gas release vent includes a plurality of gas release vents opening into said main bore substantially along the top of said main bore.
 4. The extruder of claim 1, wherein said at least one gas release vent includes a plurality of gas release vents opening into said main bore at a plurality of different angular positions around the surface of the main bore.
 5. The extruder of claim 1, wherein said main bore has a first internal diameter adjacent to said loading end and a second internal diameter adjacent to said extruding end, said second internal diameter being larger than said first internal diameter.
 6. The extruder of claim 5, wherein said main bore has a first portion extending substantially from said loading end along at least to said midpoint, said first portion being substantially cylindrical with said first internal diameter, and wherein said main bore has a second portion extending substantially from said first portion to said extruding end, said second portion having a gradually increasing internal diameter.
 7. The extruder of claim 6, wherein said second portion has a substantially conical internal surface.
 8. The extruder of claim 7, wherein said substantially conical internal surface has a conical angle of between about 1° and about 10°.
 9. A method of producing an extruded profile using an extruder including a container with a main bore, the main bore having a loading end and an extruding end separated by a length, the container being formed with at least one selectively openable gas release vent opening into the main bore at a position intermediate between the extruding end and a midpoint of the length, the method comprising: (a) introducing into the main bore a first billet; (b) forcing the first billet towards the extruding end so as to force material from the billet through a die associated with the extruding end of the bore; (c) while material from the first billet remains within the main bore, introducing a second billet into the main bore; (d) pressing the second billet towards the material from the first billet so as to cause joining of the material from the first billet and the second billet; (e) opening the at least one gas release vent so as to release gas trapped within the main bore; and (f) forcing the second billet towards the extruding end so as to force material from both the first and second billets through the die.
 10. The method of claim 9, wherein said opening is performed using a plurality of gas release vents spaced along at least one line between the extruding end and the midpoint of the length.
 11. The method of claim 9, wherein said opening is performed using a plurality of gas release vents opening into said main bore substantially along the top of said main bore.
 12. The method of claim 9, wherein said opening is performed using a plurality of gas release vents opening into said main bore at a plurality of different angular positions around the surface of the main bore.
 13. The method of claim 9, wherein the main bore has a larger internal diameter adjacent to the extruding end than adjacent to the loading end.
 14. The method of claim 13, wherein the main bore has a portion of gradually increasing internal diameter from a location between the midpoint and the extruding end extending substantially to the extruding end.
 15. The method of claim 14, wherein said second portion has a substantially conical internal surface.
 16. The method of claim 15, wherein said substantially conical internal surface has a conical angle of between about 1° and about 10°.
 17. The method of claim 9, further comprising preparing each billet prior to introduction into the main bore by removing material from at least a portion of an outer surface of the billet so as to increase smoothness of the billet.
 18. The method of claim 9, wherein the billets are aluminum billets. 